This is a continuing long-term project in which a large number of nondiabetic relatives of diabetic patients, as well as asymptomatic mildly diabetic patients are being studied periodically. We hope to learn more about the natural history of various types of diabetes mellitus from the points of view of: 1) genetics, 2) possible environmental factors, 3) carbohydrates intolerance, 4) insulin secretion, 5) other pancreatic hormone secretion, 6) occurrence of pancreatic islet cell antibodies, 7) HLA antigen types, 8) development of microangiopathy, 9) development of macroangiopathy, 10) development of neuropathy, 11) evaluation of factors which alter the expression of these manifestations.